During the recovery of hydrocarbons such as oil and gas from a reservoir formation via a production well the productivity of the well may be impaired due to formation plugging and erosion of the reservoir formation in the region of the well intake zone. In this region a large pressure drawdown of the produced fluids takes place while the velocity of these fluids through the pores of the formation is high. Under these circumstances precipitation and deposition of asphalt, heavy crude fractions, scale, salt, or sulphur may eventually lead to a large reduction in well productivity. The large pressure drawdown may further give rise to water coning, which implies that water is sucked up from a water bearing layer underneath the reservoir formation.
It is known to inject fluids, such as steam, water, solvents, and chemical inhibitors, via the production well into the well intake zone in order to alleviate production problems. These fluids may be injected via the production tubing of the well into the surrounding formation after interruption of the production operations.
It is also know that these fluids may be injected via a separate passageway in the production well to a location above the well intake zone where the fluids are injected into the surrounding formation and are expected to migrate through the formation to the well intake zone. U.S. Pat. Nos. 4,109,722, 4,109,723, and 4,362,213 disclose well systems where fluids are pumped down into the well via the annular space around the production tubing and subsequently injected into the surrounding formation via perforations in the well casing above the well intake zone. The '772 patent mentions that the depth of penetration of the injected fluid can be increased by forming an impermeable cement barrier in the formation pores around the well between the location where the fluids are injected and the well intake zone.
It is known from British patent application No. 2,194,572 to separate in a downhole separator water from crude oil and to reinject the separated water into an underlying water bearing layer via a water recirculation leg. This know well configuration does not allow injection of a special treatment or flushing fluid into the formation or to avoid water coning since the water recirculation does not result in a net water removal from the formation.
A disadvantage of the injection of fluid above the well intake zone is that the injected fluid will tend to seek the shortest path through the reservoir formation toward the underlying well intake zone so that the fluids only reach the upper part of this zone.
It is an object of the present invention to provide a method and well system for producing hydrocarbons which alleviate the problems associated with the prior art production techniques.